Methods, arrangements and apparatus for determining the position of the edge bead removal line of an object, for example a wafer, are well known from the practice. Herein, the postures and locations, in other words “positions”, of structures are determined on the object.
In semiconductor manufacture, disk-like objects (wafers) are coated with photoresist during the manufacturing process. The photoresist is first subjected to an exposure and then to a development process. It is structured in these processes for subsequent process steps. Slightly more photoresist is deposited on the edge area of the wafer than in the center of the wafer due to manufacturing conditions. This is how an edge bead is produced. Photoresist on the edge of the wafer and the edge bead can lead to the contamination of manufacturing machines and to defects on the wafer in the subsequent processing steps.
To avoid these effects, an edge bead removal (EBR) is carried out. Defects in the width of the edge bead removal result from imprecise alignment of the corresponding edge bead removal apparatus relative to the wafer. Further sources of error can be the imprecise alignment of the illumination apparatus relative to the wafer during exposure of the photoresist. Herein, an edge bead removal which is too extensive, leads to a reduction of the usable wafer area and therefore to a loss of produced chips. An edge bead removal which is too small, can lead to a contamination of the subsequently applied resist layers or other structures in the edge area of the wafer. Since in both cases the productivity of the manufacturing process is reduced, the edge bead removal, as well as many other defects, is constantly monitored during the manufacturing process. Herein both the width of the edge bead removal and whether an edge bead removal has been carried out at all are checked.
For the purpose of orientation, wafers usually have a mark on the substrate edge, a so-called alignment mark. This alignment mark can be either a notch or a flat on the wafer edge. This alignment mark allows the wafer to be unequivocally oriented.
In order to determine the position of the edge bead removal line (EBR line) of the wafer, it is necessary to determine the position of the wafer edge. Herein, however, usually neither the position of the wafer on the rotary stage nor the position of the camera line is in correspondence with the centerpoint of the rotary stage. This is why the edge bead removal line is not in correspondence with the centerpoint of the rotary stage either, which makes determination of the position of the edge bead removal line of the wafer difficult. Due to the lack of correspondence between the edge bead removal line and the centerpoint of the rotary stage, there are often imprecisions and errors in determination of the position of the edge bead removal line.
Apparatuses are known for detecting various structures on the surface of the wafer by means of image detection. Herein, the wafer is illuminated in the bright-field mode and scanned by means of a camera (matrix or line camera).
Such an inspection machine by KLA-Tencor Corporation is described in the article entitled “Lithography Defects: Reducing and Managing Yield Killers through Photo Cell Monitoring” by Ingrid Peterson, Gay Thompson, Tony DiBiase and Scott Ashkenaz, Spring 2000, Yield Management Solutions. The wafer inspection machine described there relies on an incident-light illumination means for inspecting microdefects with low contrast in a bright-field illumination mode.
Laid-open German Patent Application DE 102 32 781.5 discloses an apparatus for wafer inspection for making the line caused by the edge bead removal determinable, so that it is distinguishable from other lines or edges to be determined on the wafer.
A method for removing and for improved detection of the edge bead is known, for example, from U.S. Pat. No. 7,142,300 B2. In this document it is suggested that the contrast between the silicon layer of the wafer and the applied photoresist layer can be improved by using a specialized illumination. For this purpose, the wafer is to be illuminated separately with s- and p-polarized light in the vicinity of the Brewster angle of silicon or the photoresist layer. Subsequently, the difference between the images of the reflected s-polarized radiation and the image of the reflected p-polarized radiation is evaluated for contrast enhancement. The use of polarized light, however, requires additional optical components.
U.S. Pat. No. 7,197,178 B2 discloses a method for measuring the edge bead removal, which also includes the determination of a line or edge at the circumference of the wafer. The position of the wafer notch at the edge of the wafer and the position of the center of the wafer are determined. Also, the distance between the edge of the wafer and an edge bead removal line on the circumference of the wafer is determined. The edge bead removal line is then determined from a bright field and a dark field, the method is based, however, on a technical idea which is different from the present invention.
Laid-open German Patent Application DE 10 2005 014 594.9 discloses a method for detecting incomplete edge bead removal of a wafer, wherein first an edge area of a reference object is imaged. Marks are defined in the edge area of the reference object. Finally, images of edge areas of a plurality of objects of one lot are recorded. The inspection of the objects is exclusively limited to the positions of the marks defined on the reference object. The use of reference objects and a plurality of lots is, however, complex.
Laid open German Patent Application DE 10 2005 018 743.9 discloses a method for imaging the edge of a wafer with a suitable method, in particular, in a dark-field image on a suitable detector, such as a line camera. The lines or edges present on the wafer edge are detected, and then a decision process is carried out to identify an edge bead removal line.
German Patent DE 10 2005 028 427 discloses a method for optically imaging a wafer with a photoresist layer, wherein an imaging area on the surface of the wafer is illuminated with light and a fluorescence image is recorded of the imaging area on the basis of the fluorescent light emitted by the excited light due to the illumination. The evaluation method is very complex, however, when fluorescent light is used.
German Patent DE 10 2004 029 012 discloses a method for inspecting the edge bead removal of a wafer, wherein an optical image of the area to be inspected is recorded, wherein first a first optical image is recorded prior to the application of a layer on the wafer disk and then a second optical image is recorded after the at least partial removal of this layer, and then the imaged area of the wafer surface is inspected by comparing the first and the second image.
As already mentioned above, in the arrangements, apparatuses and methods from the prior art in the field of wafer inspection, the position of the edge bead removal line of a wafer is determined in a relatively complex way (comparison of reference images) or as an approximation. As the requirements with respect to precision become more stringent, it is increasingly doubtful that the position of the edge bead removal line can be determined with sufficient precision, which is why more general approaches are required.